ABSTRACT
The role of the Indonesian Seas in climate is attributed to the intense mixing observed throughout the region. Mixing cools the surface temperature and hence modifies the atmospheric convection centered over the region. Mixing also controls the heat exchange between the Pacific and Indian Oceans by transforming water-mass properties while they transit through the region. Mixing in the Indonesian Seas has long been identified to be driven locally by tides. Here we show that the observed mixing can also be powered by the remotely generated planetary waves and eddies. We use a regional ocean model to show that the Indonesian Seas are a sink of the energy generated in the Indian and Pacific Oceans. We estimate that 1.7 GW of the remotely generated energy enters the region across all straits. The energy flux is surface intensified and characterized by a convergence, implying dissipation and mixing, within the straits and along topography. Locally, energy convergence associated with this process is comparable in magnitude to tidal energy dissipation, which dominates the deep ocean.
ABSTRACT
Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise.
ABSTRACT
Mass loss from the West Antarctic ice shelves and glaciers has been linked to basal melt by ocean heat flux. The Totten Ice Shelf in East Antarctica, which buttresses a marine-based ice sheet with a volume equivalent to at least 3.5 m of global sea-level rise, also experiences rapid basal melt, but the role of ocean forcing was not known because of a lack of observations near the ice shelf. Observations from the Totten calving front confirm that (0.22 ± 0.07) × 106 m3 s-1 of warm water enters the cavity through a newly discovered deep channel. The ocean heat transport into the cavity is sufficient to support the large basal melt rates inferred from glaciological observations. Change in ocean heat flux is a plausible physical mechanism to explain past and projected changes in this sector of the East Antarctic Ice Sheet and its contribution to sea level.
